Fail safe locking mechanism for fluid operated valve actuator

ABSTRACT

A fail safe mechanism is provided for locking an actuating piston rod of a fluid operated actuator in a selected axial position in the event of a failure, or significant decrease in, the fluid pressure applied to the actuator. Preferably, a secondary cylinder is provided within the actuator cylinder and is in fluid communication therewith. A piston in the secondary cylinder is biased toward a locking position by a spring and is shiftable toward a released position by the existence of a predetermined amount of fluid pressure in the main cylinder. An annularly extending locking mechanism is provided in surrounding relationship to the actuating piston rod and is radially movable into engagement with a locking shoulder on such piston rod when the rod is shifted to one of its selected axial positions by the application of fluid pressure to the cylinder. In its locking position, the locking piston prevents any radial outward movement of the annularly extending locking means and thus mechanically locks the actuating piston rod in its selected axial position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a novel locking mechanism for locking thepiston rod of a fluid responsive valve actuator in at least one of firstand second positions respectively corresponding to the open and closedpositions of a valve member manipulated by the actuator.

2. Description of the Prior Art

In oil fields, pipe lines, and refineries there has been a considerableneed for a fluid actuated valve actuator which, in the event of anemergency causing the reduction or loss of control pressure supplied tothe actuator, would be mechanically locked in the position it held priorto the occurrence of the emergency. Depending upon the particularapplication, it may be desirable that the fluid operated valve actuatorbe mechanically locked in either its open or its closed position. Moreimportantly, there are a significant number of valves requiring cyclingoperations between an open and closed position and it is desirable thatsuch valves be locked in the same position as existed prior to theoccurrence of the particular emergency. In a more common parlance, it istherefore desirable that a valve actuator be capable of being locked inan up position, a down position, or either an up or down position in theevent of loss of, or reduction in, control pressure supplied to suchvalve actuator.

SUMMARY OF THE INVENTION

The fail safe mechanism of this invention may be applied to any type offluid actuator, either hydraulic or pneumatic, which incorporates acylinder to which fluid pressure is applied, and a piston axiallyshiftable within such cylinder by the applied pressure. Customarily, thepiston has at least one axially extending rod portion extendingoutwardly through an annular seal in the end wall of the cylinder toprovide a means for connecting the pistion rod to a valve or othermechanism requiring actuation. A secondary cylinder chamber is providedwithin the main cylinder and in fluid communication with the maincylinder chamber. A locking piston is mounted for reciprocal movementsin the secondary cylinder respectively between a locking position and arelease position. The application of fluid pressure to the main cylindernormally moves the locking piston to its release position. Resilientmeans, such as a spring, is provided to bias the locking piston to itslocking position so that any failure of pressure in the main cylinder orsignificant reduction in such pressure will cause the locking piston tomove to its locking position.

The actual mechanical locking of the piston rod in a selected axialposition is accomplished by an annularly disposed array of eitherlocking segments or locking balls which are radially shiftable to moveinto locking engagement with a shoulder provided on the main piston rodwhen such rod is in one of its desired axial positions. The lockingelements may be moved radially inwardly either by resilient means or bythe camming action of the locking piston as it moves to its lockingposition.

In the event of a loss of fluid pressure in the main cylinder, or asignificant decrease in such pressure, the annular array of lockingelements move into engagement with the locking shoulder on the mainpiston rod and are retained in such position by the movement of thelocking piston to its locking position under the influence of itsbiasing spring.

Obviously, such locking mechanism may be applied to a single actingvalve actuator to hold the actuator in an up position, or a downposition. By providing two locking mechanisms within the main cylinder,which may be located on opposite sides of the piston, a double actingactuator may be provided with fail safe locking in both its up and downpositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, with a portion thereof shown in verticalsection, of a double acting hydraulic cylinder incorporating the lockingmechanisms of this invention, with the piston of the cylinder shown inone of its two axial positions.

FIG. 2 is a view similar to FIG. 1, but showing the piston in the otherof its axial positions.

FIG. 3 is a view similar to FIG. 1 of a double acting hydraulic cylinderincorporating a modified locking mechanism in accordance with thisinvention.

FIG. 4 is a view similar to FIG. 3 but showing the piston in theopposite axial position from that shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fluid operated actuating device 1 is shown in all of the FIGS. asincorporating a hollow cylinder portion 10 cooperating in slidablerelationship with a piston 20 which is mounted on and secured to apiston rod 21 in any conventional manner.

While in all of the illustrated embodiments, a double acting piston andcylinder unit is illustrated, wherein fluid pressure is selectivelyapplied to either side of the piston 20 and the extreme axial ends 30aand 30b of the piston rod 21 respectively pass outwardly of the endwalls of the device through suitable annular seals, those skilled in theart will readily recognize that the principles of this invention areequally applicable to a single acting piston and cylinder arrangementwherein pressure is applied to only one side of the piston and thepiston rod extends axially through only one end wall of the cylinder.Thus, the invention is equally applicable to both single actingactuators and double acting actuators.

The cylinder 10 comprises a main tubular body portion 11 havinginternally threaded end portions 11a and 11b for reception of threadedportion 41a and 42a respectively of hollow bushings 41 and 42 which areinserted within the ends of the cylinder 10. The axially outer end ofthe bushing 41 is internally threaded to receive an externally threadedportion 43a of an end wall bushing 43. Likewise, the bushing 42 isinternally threaded as indicated at 42b to receive the externallythreaded portion 44a of the end wall bushing 44. The cylindrical bores44b of the end wall bushing 44 incorporate a conventional seal 44c whichsealingly engages the rod portion 21b of the piston assembly 20.Similarly, a seal 43c provided in the bore 43b of the opposite end wallbushing 43 sealingly engages the rod portion 30a of the piston rod 21.

The piston 20 includes a head portion 20a incorporating a suitable seal20b which slidably and sealably engages the interior wall 11a of thecylinder tube 11. Pressured fluid may be supplied through conventionalfittings to the interior of the cylinder 10 on either side of the piston20 and thus the piston assembly 20 may be shifted axially between eitherof two selected axial positions respectively determined by the abutmentof a shoulder 20c provided on the piston head 20 with an interiorlyprojecting radial wall 41c provided on the bushing 41 (see FIG. 1), andby the shoulder 20d abutting a similar interiorly projecting radial wall42c provided on the bushing 42. (See FIG. 2). Interiorly projectingwalls 41c and 42c are not in sealing engagement with the adjacentportions of the piston rods 30a and 30b respectively, hence theseinteriorly projecting walls each define annular secondary cylinderchambers 45 and 46, respectively, which are in fluid communication withthe interior of the main cylinder 11.

Within such secondary cylinders, identical annular piston elements 50are respectively mounted for sliding engagement relative to the interiorcylindrical walls 41d and 42d of the respective end bushings 41 and 42.Pistons 50 are provided with internal seals 50a respectively engagingthe adjacent surfaces of the piston rod 30a and 30b and external seals50b respectively engaging the internal surfaces 41d and 42d of the endbushings 41 and 42. Thus, when pressure is applied to one side of thepiston 20, causing it to move to the left as viewed in FIG. 1, then thepiston 50, mounted in secondary cylinder chamber 46, is shifted axiallyto the right by the same fluid pressure applied to the main piston 20.This axially outward position, illustrated in FIG. 1, will hereinafterbe referred to as the release position.

As the piston 20 approaches its extreme lefthand position, asillustrated in FIG. 1, the piston 50, which is mounted in the secondarycylinder chamber 45, remains in its illustrated right or inward positiondue to the influence of an axially disposed biasing spring 52. Thisposition of each piston 50 is hereinafter referred to as the lockingposition of the locking pistons 50. When fluid pressure is applied tothe interior of the cylinder 10 on the opposite side of the piston head20a, the positioning of the locking pistons 50 are reversed and thepiston 50 disposed in the secondary cylinder chamber 45 is moved axiallyoutwardly to its release position, while the piston 50 disposed in thesecondary cylinder chamber 46 is maintained in the axially inwardlocking position by its biasing spring 52.

A pair of locking shoulders 33 are respectively provided on rod portions30a and 30b in axially spaced relationship on the piston rod 21 and onopposite sides of the piston head 20a. Locking shoulders 33 are axiallypositioned so as to be respectively adjacent the inner ends of thelocking pistons 50 when the piston unit 20 is in one or the other of itstwo extreme axial positions.

Two annular arrays of locking elements 25 are provided whichrespectively cooperate with the locking shoulders 33 to secure thepiston assembly 20 in one of its extreme axial positions whenever thereis a loss of, or a significant decrease in, pressure applied to thefluid pressure actuator 10.

In the modification of this invention illustrated in FIGS. 1 and 2, thelocking elements 25 comprise an annular row of balls. One set of suchballs are retained within an annular chamber defined by a recess 50cprovided on the adjacent portion of the locking piston 50 and the innerwall 41e of the internally projecting radial flange 41c provided on thecylinder bushing 41. At the other end of the cylinder, the inner surface42e of the internally projecting radial flange 42d cooperates with thepiston recess 50c to provide a holding chamber for the other set oflocking balls 25. The inner end face of each piston 50 is provided withan inclined surface 50e so as to urge the locking balls 25 inwardly intolocking engagement with locking shoulder 23 on the piston assemblage.Each locking shoulder 33 is similarly inclined so as to cam the lockingballs 25 out of its path any time that they are not restrained againstradially outward movement by the locking piston 50.

From the foregoing description, it is therefore apparent that theannular array of locking balls 25 is freely radially shiftable into alocking engagement with the shoulder 33 provided on the piston rod 21.So long as pressure is applied to the actuator 10 on a particular sideof the piston assemblage 20, the locking balls 25 on that side will bein their release position since the respective locking piston 50 will beforced axially to its release position, thus permitting the balls 25 tomove radially outwardly and roll freely on the cylindrical surface ofthe piston rod 30a or 30b, as the case may be. When the pistonassemblage 20 is in its extreme axial position, either to the left, asillustrated in FIG. 1, or to the right, as illustrated in FIG. 2, theloss of pressure within the actuator 10, or a significant decrease insuch pressure, will cause a corresponding drop in pressure in therespective secondary cylinder 45 or 46 and will cause an axially inwardshifting of the respective locking piston 50 under the bias of therespective spring 52. Such axial movement causes a radially inwarddisplacement of the annular array of locking balls 25 into engagementwith the adjacent one of the locking shoulders 33 provided on the pistonrod portions 30a or 30b.

Thus, the piston rod assemblage 21 is physically locked in either of itsextreme axial positions to which it is moved through the application ofpressure to one side or the other of the piston head 20a. Hence, theoccurrence of any emergency resulting in a loss of control pressure toactuator 10 or a significant decrease in such pressure, will not permitthe fluid actuator 10 to move out of the position that it held at thetime prior to the existence of the emergency.

Of course, the rod assemblage 21 may be unlocked from either of thelocked positions by providing auxiliary or line pressure means to act onthe portion of the piston 20 facing the respective locked assemblage 21,and the respective secondary piston 50 will be shifted axially away fromthe piston 20 to permit the balls 25 to become disengaged from thecammed shoulders 33.

Referring now to the modification disclosed in FIGS. 3 and 4, similarreference numbers refer to similar parts as described above inconnection with FIGS. 1 and 2. In this modification, the annular arrayof locking elements comprises an annular group of locking segments 26,which are mounted in the same spaces as defined above, respectivelyprovided between the ends of the locking pistons 50 and the adjacentface 41e or 42e of the radial internal shoulders of the end bushings 41or 42. The segments 26 are each provided with a circumferentiallyextending groove 26a in which a tension spring 27 is mounted to providea continuous bias urging the segments 26 to move radially inwardly. Thespring, however, is not absolutely essential, for each locking segment26 is also provided with a camming surface 26b, which is engaged by theinclined end surface 50e provided on the locking pistons 50, and thecooperation of these inclined cam surfaces will force the lockingsegments 26 radially inwardly into engagement with the locking shoulders33.

The principles of this invention may be readily applied to any singleacting fluid actuator wherein the piston rod of the actuator is moved bythe application of fluid pressure to one extreme axial position. Only asingle locking mechanism embodying this invention need by incorporatedin the single acting actuator, but it will be effective, on any loss of,or significant decrease in, the control pressure applied to theactuator, to lock the single acting actuator in the position that itoccupied prior to the reduction in control pressure.

Obviously, the fluid actuators may be either hydraulically orpneumatically operated.

Locking mechanisms embodying this invention find ready application forthe control of relatively massive valves employed in oil wells, pipelines and refineries. Utilization of a fluid actuator embodying thelocking mechanisms of this invention will permit the particular valve towhich the actuator is applied to be locked in either its open or itsclosed position on the occurrence of any failure in control pressure, ora significant decrease in such control pressure. Thus, a single actingfluid actuator may be locked in its "up" or open position or its "down"or closed position. If a double acting fluid actuator is employed, itwill be locked in either its up or down position, depending on whichposition the actuator was in at the time of the occurrence of theemergency.

Although the invention has been described in terms of specifiedembodiments which are set forth in detail, it should be understood thatthis is by illustration only and that the invention is not necessarilylimited thereto, since alternative embodiments and operating techniqueswill become apparent to those skilled in the art in view of thedisclosure. Accordingly, modifications are contemplated which can bemade without departing from the spirit of the described invention.

What is claimed and desired to be secured by Letters Patent is:
 1. In afluid operated, double acting cylinder having a main cylinder, a pistonhead reciprocable therein, an actuating piston rod extending through anend wall portion of the main cylinder, and means for selectivelysupplying pressured fluid to said cylinder on opposite sides of saidpiston head to shift said piston head and rod to either of their extremeaxial positions relative to the cylinder, the improvement comprising:means in said end wall portion of said main cylinder defining asecondary cylinder chamber in direct fluid communication with one end ofsaid main cylinder; a locking piston mounted for reciprocable axialmovements in said secondary cylinder chamber between a release positionand a locking position, said locking piston being shiftable to saidrelease position by pressured fluid supplied to the adjacent portions ofsaid main cylinder; means on said piston rod defining a locking shoulderwhich is movable to a position adjacent said locking piston when saidpiston rod reaches its extreme axial position adjacent said end wallportion; freely shiftable locking means movable into lockingrelationship with said piston rod locking shoulder to prevent reversemovement of said piston rod from said extreme axial position; means onsaid locking piston for holding said locking means in locking positionrelative to said locking shoulder when said locking piston is in itssaid locking position; and means for shifting said locking piston to itssaid locking position whenever said locking means moves into engagementwith said locking shoulder of said piston, thereby locking said pistonrod in said selected extreme position, said main cylinder being providedwith a second end wall portion axially spaced from the first mentionedend wall portion; means in said second end wall portion defining atertiary cylinder chamber in direct fluid communication with the otherend of said main cylinder; a second locking piston mounted forreciprocal axial movements in said tertiary chamber between a releaseposition and a locking position; said second locking piston beingshiftable to said release position by pressured fluid supplied to theadjacent portions of said main cylinder; means on said piston roddefining a second locking shoulder which is movable to a positionadjacent said second locking piston when said piston rod reaches itsother extreme axial position adjacent said second end wall portion;freely shiftable second locking means movable into locking relationshipwith said second locking shoulder to prevent reverse movement of saidpiston rod from its said other axial position; means on said secondlocking piston for holding said second locking means in lockingposition; and means for shifting said second locking piston to its saidlocking position whenever said actuating piston rod is shifted to itssaid other extreme axial position, thereby locking said actuating pistonrod in said other extreme axial position, said secondary cylinderchamber and said tertiary cylinder chamber each having an annularconfiguration with said piston rod defining the inner wall thereof andsaid first and second locking pistons being respectively slidable onsaid piston rod in sealing relationship therewith.